From experience: Scoundrel healing is laughable (2 stack of HoT on everyone, use your instas, and you don't even have to stop to cast, so just run around like a headless chiken), Sage is a bit tricier, but doable too. I've done it just yesterday night on my 'mando healer alt. I'd give advice on what abilities to use, but I cannot really remember*. I had to make a 12-min-long phonecall (mobile between the neck and shoulders to make it more interesting
) after the droid boss and by the time I was done, we've just finished the whole FP (and yes, it was HM,). Avoiding red circles and watching out who had eaten them is pretty much on autopilot at this point. Dunno if it helps, but I'm usually jumping out of the circles too. It all boils down to practice, if you're game is too laggy for you to avoid them (I'm running between 80-300ms), then simply never stop running, only stop and cast a heal, when you see the red circle at someone else's feet.
If you're the healer it can hardly go wrong. Enrage is not that tight, in case the dps decides to eat 3 circles in a row (which is hard to heal through, unless you're a scoundrel), then just finish it with the tank.
However a few days ago when I was on my shadow tank, unfortunately the other three bit the dust from the circles. At that point Zokar tries to get you with cryo grenade and red circle too. Finished him from 7-10%, never eating a single circle. So my advice: practice, parctice, parctice and never give up, cheers
* Thinking about it a little: throw kolto bomb to hit everyone for the healing buff, use all other heals when this buff is up on others, use your 360° knockback for aoe heals, keep up the healing stacks on the tank always, use your no cast time and free cast ability, don't save the insta heal for emergencies, use it on CD, go super healer mode after 30 stacks only when it is required. And when something goes really amiss (tank fails to turn boss, adds are not gunned down fast, too much damage going on), don't try to save you energy on the brink of crappy regen, just go all out and pop your energy back ability. Hope this helps.
(Sorry for the lack of ability names, my 'mando is really not my main, and you would need the Merc ability names anyway.)